The invention relates to tension control devices for a printing press.
Before the present invention, multi-color printing units have been used in a printing press to print colored images on a paper web. The webs used in the press unwind the web from a supply roll, and may be centered on the rollers of the press or may be positioned off-center. Due to the relatively fast speed of the press, the rolls have been completely unwound in a relatively short period of time, such as 15 minutes.
In accordance with prior practice, a new roll of the web is pasted onto the web of the previous roll when it is almost depleted. However, the rolls each have different characteristics, such as different manufacture and different winding tensions. As a result, the tension on opposed sides of the new web becomes significantly different, causing loss of registration in the press and flapping of the web, which may cause a web break.
Adjustments must be made to the press in the event of loss of registration, and due to the relative frequency of web pasting. Such adjustments result in loss of press time, wasted product, and inconvenience to the operator of the press.
In accordance with certain aspects of the present invention, a tension control device is provided for a printing press. The device includes an adjustment roller, with a web of the press passing from a supply roll of the web to the adjustment roller. Means are provided for measuring the tension on opposed sides of the web passing downstream from the adjustment roller. Means responsive to the measuring means are provided for automatically approximately equalizing the tension of the web by adjustment of the adjustment roller on one end only of the adjustment roller.
In accordance with additional aspects of the present invention, a tension control device is provided for a printing press. The device includes an adjustment roller and a tension roller positioned downstream of the adjustment roller, with a web of the press passing from a supply roll to the adjustment roller and tension roller, wherein the web is positioned off-center with respect to the adjustment roller and tension roller. Means are provided for measuring the tension on opposed ends of the tension roller, wherein a tension differential is detected at the opposed ends of the tension roller when the tension at opposed sides of the web are substantially equal. Means responsive to the measuring means are provided for automatically approximately equalizing the tension at opposed sides of the web by adjusting the adjustment roller on one end only of the adjustment roller to maintain the tension differential.
In accordance with further aspects of the present invention, a tension control device is provided for a printing press having a web. The device includes an adjustment roller and a tension roller located downstream of the adjustment roller, wherein the web passes over the adjustment roller and tension roller. A pair of transducers are provided for measuring tension at opposed ends of the tension roller, and means are provided for adjusting one end only of the adjustment roller. A controller controls the adjusting means in response to the transducers to approximately equalize tension on opposed sides of the web.